There are many many advantages to using object oriented programming in plugins; however, if you don’t want to use OOP, I would suggest either setting a global variable or defining a constant with the value you want to use for that string.

You can call get_admin_page_title(). If the global variable $title is not empty it will return that, otherwise it will set it and return the value.

It is called at the top of admin-header.php and then goes through esc_html(), so if you want the raw value you should empty $title and call the function again.